This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-123540, Apr. 25, 2000; and 2000-323208, Oct. 23, 2000, the entire contents of both of which are incorporated herein by reference.
The present invention relates to a worktable device and plasma processing apparatus which process a target substrate such as a semiconductor wafer or a glass substrate (LCD substrate) for a liquid crystal display (LCD) in a semiconductor process. The term xe2x80x9csemiconductor processxe2x80x9d used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or an LCD substrate, by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
As a plasma processing apparatus for the semiconductor process, for example, a CVD apparatus, etching apparatus, or ashing apparatus is known. The plasma processing apparatus has a hermetic process chamber in which a plasma is to be generated, and a worktable (wafer chuck) on which a target substrate such as a wafer is to be placed in the process chamber.
FIG. 9 is an enlarged sectional view schematically showing part of a conventional worktable structure. As shown in FIG. 9, a wafer W is placed on the main surface of a worktable 91, and a focus ring 92 made of a conductive or insulating material is placed on a sub-surface around the main surface so as to surround the wafer W. A cooling mechanism for cooling the wafer W is disposed in the worktable 91.
When the wafer W is to be subjected to a plasma process, the wafer W is fixed on the worktable 91, the process chamber is held at a predetermined vacuum degree, and a plasma is generated in the process chamber. Ions in the plasma are attracted onto the wafer W by the self bias produced on the worktable 91 side. Thus, the wafer W can be subjected to a predetermined plasma process (e.g., an etching process).
As the temperature of the wafer W is increased by etching, the wafer W is cooled by using the cooling mechanism through the worktable 91. In this case, a backside gas such as helium (He) gas with a good thermal conductivity is supplied between the upper surface of the worktable 91 and the lower surface of the wafer W, so that the heat transfer efficiency between the worktable 91 and wafer W is increased.
In the structure shown in FIG. 9, the focus ring 92 cannot be cooled in the same manner as the wafer W. The focus ring 92 is accordingly heated over time to a temperature much higher than that of the wafer W, and the temperature of the periphery of the wafer W becomes higher than that of the inner side of the periphery. As a result, the etching characteristics degrade on the periphery of the wafer W, leading to problems such as degradation in hole penetration properties or etching selectivity. Hole penetration properties are the characteristics in that the wafer can be reliably etched to a predetermined depth. Poor hole penetration properties mean that penetration is not sufficient and the wafer cannot be etched to a predetermined depth.
In particular, recently, an increase in diameter and micropatterning degree of the wafer W progress remarkably, and attempts have been made to eliminate waste in a single wafer W so that as many devices as possible can be obtained. For this purpose, devices are formed up to immediately near the edge of the wafer W, and temperature increase of the focus ring 92 greatly influences the yield of the device.
It is an object of the present invention to provide a worktable device and plasma processing apparatus for a semiconductor process, which can process a target substrate with a high planar uniformity without accompanying a change over time.
According to the first aspect of the present invention, there is provided a worktable device for a semiconductor process, which comprises
a worktable having a main surface for supporting a target substrate and a sub-surface disposed around the main surface,
a cooling mechanism disposed in the worktable and configured to supply cold to the main surface and the sub-surface,
a focus ring placed on the sub-surface and configured to surround the target substrate on the main surface, and
a heat transfer medium interposed between the sub-surface and the focus ring, the heat transfer medium being so disposed as to improve thermal conductivity between the sub-surface and the focus ring to be higher than in a case with no thermal transfer medium.
According to the second aspect of the present invention, there is provided a plasma processing apparatus for a semiconductor process, which comprises
a hermetic process chamber,
a supply system configured to supply a process gas into the process chamber,
an exhaust system configured to vacuum-evacuate an interior of the process chamber,
an excitation mechanism configured to excite and plasmatize the process gas,
a worktable disposed in the process chamber and having a main surface for supporting a target substrate and a sub-surface disposed around the main surface,
a cooling mechanism disposed in the worktable and configured to supply cold to the main surface and the sub-surface,
a focus ring placed on the sub-surface and configured to surround the target substrate on the main surface, and
a heat transfer medium interposed between the sub-surface and the focus ring, the heat transfer medium being disposed so as to improve thermal conductivity between the sub-surface and the focus ring to be higher than in a case with no thermal transfer medium.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly point out hereinafter.